1. Field of the Invention
The present invention relates to a grounding switch that is incorporated in gas insulated switchgear.
2. Description of the Related Art
A grounding switch is incorporated in gas insulated switchgear (GIS). The grounding switch is used as a contact in grounding of a main circuit when testing equipment, or as an earth terminal when measuring equipment. When grounding a main circuit, typically, a moving contact, which is grounded, is moved along a center axis of the grounding switch so as to be inserted into a high-voltage electrode, which is connected to high voltage. If, by any possibility, the moving contact moves in an axial direction of the grounding switch and is inserted into a high-voltage electrode as the result of an erroneous operation when high voltage is being applied to the main circuit, there has been a need of a function which is capable of opening the grounding switch afterwards with a reliable earth connection taken and without fusing across electrodes. This is to say that if the moving contact erroneously enters into the high-voltage electrode in a state where a high voltage is applied, an arc occurs due to breakdown of insulation between the electrodes. The surrounding gas therefore reaches a high temperature and the gas pressure rises abruptly. Gas for which the pressure has abruptly risen then acts as a repulsive force on the moving contact during operation. When operation of the moving contact continues so that the high-voltage arc contact and the moving arc contact make contact, frictional resistance occurs between the electrodes and there is further repulsive force exerted on the moving contact. In Japanese Utility Model Application Publication S50-46947, one contact piece of a number of arranged contact pieces (high-voltage main contacts) extends in the direction of a center axis, with a tip of the one contact piece constituting an arc-focusing contact (high-voltage arc contact).
This means that surrounding gas is heated and expands as a result of an arc occurring across the moving arc contact and the high-voltage arc contact. However, gas that has increased in temperature does not cool instantaneously directly after the arc is extinguished and the pressure of the gas that has risen abruptly does also not return to its original state instantaneously. At this stage, the moving contact is subject to two repulsive forces at the same time, repulsive force due to hot gas caused by arcing, and repulsive force due to frictional resistance. A substantial mechanical burden is therefore placed on the operation of the drive mechanism.
In the structure shown in FIG. 1 of Japanese Utility Model Application Publication S50-46947, a fixed angle taper is provided from the tip of the arc-focusing contact to the main contact section. This means that the moving contact continues to be subject to a substantial repulsive force in the direction of insertion as a result of substantial frictional resistance between the contacts directly after the moving contact makes contact.